Although I do agree about the of Titan and warlock being a guaranteed kill(s) when it comes to supers, (especially the Titan who is invulnerable to shotguns and direct rockets to the face during the "hulk smash" animation, damn that's infuriating!!) try to remember that supers arnt available all of the time to players. And also, (I play as a hunter btw) I don't think that the melee is supposed to be equal for all classes. The best idea is to try and not let the physically stronger character get near you, or at least have them unaware while you use the shotgun/knife combo.